The present invention is directed to a communication device, such as a selective call receiver, and more particularly to an efficient communication device and method of correlation detection using a low cost and low power hardware architecture.
The Maximum Likelihood Detector which is also known as the Optimum Noncoherent Detector (or correlation detector) for detecting FSK signals in an additive white gaussian noise channel is well known. The performance of a correlation detector can also be achieved with other detector architectures such as a Matched Filter or a Fast Fourier Transform (FFT). However, use of these detectors to achieve a significant sensitivity improvement (i.e., 4 dB) over that of discriminators for 4-level orthogonal signaling (i.e. FLEX(trademark)) and a significant sensitivity improvement (i.e., 3 dB) for 4-level quasi-orthogonal signaling (i.e. ReFLEX(trademark)) depends greatly on the hardware implementation to allow for the practical realization of the specific architecture. The reasons for this is that performing such functions in hardware can become quite complex, costly, and power consuming involving many multiplication and squaring functions. Thus, what is needed is a new correlation detector scheme that can achieve up to 4 dB of sensitivity improvement for 4-level orthogonal signaling for FLEX(trademark) (for example) and up to 3 dB of sensitivity improvement for quasi-orthogonal signaling for ReFLEX(copyright) (for example) over discriminator based detectors using low cost and low power solutions. Ideally, the new correlation detector scheme can also be applied to MSK signaling used in GSM.